Dropout electrical fuse

ABSTRACT

A high voltage circuit interrupter construction in which first fusible means are disposed on an insulating core within a fuse tube, second fusible means are disposed within the core, opposite corresponding ends of both means being electrically interconnected, one end of the second fusible means being attached to a releasable conductor which conductor is releasable upon melting of the second fusible means, and an axially movable member secured to the conductor operative to dislodge the conductor from the core upon fusion of the second fusible means.

United States Patent 1 1 1111 3,852,696

Cameron Dec. 3, 1974 [5 DROPOUT'ELECTRICAL FUSE 3,447,114 5/1969 Frink et al. .1 337/171 [75] lnventor: Frank L. Cameron, lrwm, Pa. Primary Examiner jl D- Miller [73] Assignee: Westinghouse Electric Corporatio Assistant Examiner-Fred E. Bell Pittsburgh, Pa. Attorney, Agent, 0r'FirmL. P. Johns 22 F] d: 0 t. 10 1973 l l c 157 ABSTRACT lzl] Appl 405l96 A high voltage circuit interrupter construction in which first fusible means are disposed on an insulating [52] US. Cl 337/240, 337/171, 337/178, Core within a fuse tube, second fusible ans ar dis- 337/194, 337/21 1, 337/239 posed within the core, opposite corresponding ends of [51] Int. Cl. l-lOlh 85/36 both means being electrically interconnected, one end [58 Field of Search 337/168, 171, 175, 178, of the Second fusible means being attached to releas- 337/194, 211, 238, 239 240 able conductor which conductor is releasable upon melting of the second fusible means, and an axially [56] Ref Cit d movable member secured to the conductor operative UNITED STATES PATENTS to dislodge the conductor from the core upon fusion 2,614,148 10/1952 Crump cl a1; 337/171 x Ofthe Second fuslble 2,62],27U 12/1952 Edwards 337/l90 8 Claims, 5 Drawing Figures PATENTEL 953 31974 sum 1 or 2 1 DROPOUT ELECTRICAL'FUSE BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to circuit interrupters and more particularly to dropout fuses.

2. Description of the Prior Art A dropout fuse structure is disclosed in U.S. Pat. No. 3,44 7,l 14. Although fuses of that type have proven reliability, they involve a complicated structure for providing a loadable release mechanism for use as a dropout fuse. That is particularly true for the extension of fuse ratings to higher voltages where there are allotted space requirements, and where it is necessary to combine the dropout fuse construction with the currentlimiting type of fuse.

SUMMARY OF THE INVENTION It has been found in accordance with this invention that the requirements for a current-limiting dropout fuse are satisfied by the provision of a fuse structure comprising an insulating casing, an insulating core within the casing, the core having a first bore therethrough, aplug in each end of thebore, each plug having opening means communicating with the exterior of the core, first fusible means extending through the bore and having opposite end portions secured to the corresponding plugs, second fusible means mounted on the exterior of the core and having opposite end portions secured to the corresponding plugs and operatively connected to corresponding end portions of the first fusible means, a first end portion of the first fusible means extending into the opening means, a conductor connected to said first end portions and extending outwardly from the plug, and an axially movable member secured to the conductor operative to dislodge the conductor from the plug upon fusion of the first fusible means.

The advantage of the dropout fuse structure of this invention is the length of the fuse is shortened by incorporating the release mechanism in the body of the fuse. Moreover, by providing for shear rather than tensile loading of the resistance wire not only is a greater loading force for smaller resistance element obtained, but fuses of lower full load rating can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side'elevational view of a current limiting dropout fuse in accordance with the invention;

FIG. 2 is a plan view of the fuse of FIG. 1;

FIG. 3 is a vertical sectional view of the views taken on the line Ill-III of FIG. 4;

FIG. 4 is a bottom plan view taken on the line IV--IV of FIG. 3; and

FIG. 5 is an enlarged fragmentary view of the plug at the lower end of the fuse.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the particular embodiment of the invention disarms 12 and 13 impose tension on the fuse 14 and sepaclosed in the drawings, a fuse structure is generally indicated at 10 (FIG. 1) and comprises an electrical insulator ll, relatively movable contactarms l2 and 13 which support a current-limiting dropout fuse 14 that electrically interconnects the arms.

The fuse structure 10 also includes line terminals 16 and 17 individually corresponding to the contact arms rate the free ends above a fusible strain element 18 when the element is melted or softened by heat of an overload current in the power transmission line. To provide tension in the fuse 14 the contact arm 12 is biased downwardly or away from the contact arm 13 in asuitable manner such as by an electrical conducting spring means 15. Thus, the spring means 15 affords a pivot for displacement of the contact arm 12 relative to the arm 13. The contact arm 13 preferably is substan-. tially fixed in position in relative to the insulator 11. For a more complete description of the fuse structure 10 reference is made to U.S. Pat. No. 2,621,270.

For the particular fuse 14 disclosed in this invention the outer end portion of the contact arm 13 includes an integral slot 13a (FIG. 2) which is adapted to receive a stud shaft 20 at the upper end of the fuse 14. Suitable means such as a wing nut 21 may be provided for retaining the stud shaft 20 (FIG. 3) in place in the slot 13a. i i

In accordance with this invention the fuse 14 (FIG. i

3) comprises a fuse tube or casing 22, a core 23, a fuse element 24, and the fusiblestrain element 18.,The fuse tube 22 is composed of a-suitable insulating material such as filament-wound glass epoxy, and is provided with ferrules 25 and 26 at each end. The ferrule 25 at the upper end includes the threaded stud 20 and is secured in a suitable manner such as by a cement and/or mechanical crimping to the end portion of the fuse tube 22. The interior of the tube 22 is filled with a mixture 27 of sand for the'purpose of subduing any arcs or vapors evolved when the fuse element 24 melts. The mixture 27 of sand is disposed between the fuse tube 22 and the core 23 and inside the cylindrical hole in the core 23.

The core 23 is substantially coextensive with the fuse tube 22, is composed'of an electrically insulating material, and has a cruciform cross-section (FIG. 4). The core 23 includes a longitudinal bore 28. The upper and lower ends of the bore 28 are closed by plugs 29 and 30, respectively, which are composed of electrically insulating material such as nylon.

The fuse element 24 consists of a strand of a plurality (preferably five) wires 24 having a high coefficient of electrical conductivity such as silver. The wires 24 are wound spirally around the end of the radially extending portions of the core 23. Opposite ends of the several wires comprising the fuse element 24 are-twisted together and secured by crimping at 31 and 32 to annular contacts 33 and 34, respectively. The upper end portion of the twisted wires 24 are disposed between the fuse tube 25 and the ferrule 25. Likewise, the lower end portion of fuse element is disposed between the ferrule 26 and the fuse tube 22. Thus, there is a conductive path through the ferrule 25, the fuse element 24, and the ferrule 26.

Each of the several wires comprising the fuse element 24 include an end portion having a larger diameter (such as 0.01 13 inch), an intermediate portion having a smaller diameter (such as 0.010 inch), and another end portion having a larger diameter (such as 0.0126 inch), each wire has-a stepped structure. The end portions of larger diameter of each wire 24 are joined together by suitable means such as a thermal weld. The fuse element 24 including'the five separate wires comprise a fuse possessing a full load rating of 25 amperes. Each of the wires 24 includes a small surface coating or spot at the center consisting of pure tin to provide the fuse element with a lower minimum melting characteristic and to'improve the low current clearing ability of the device.

The wires of the fuse element 24 are wound spirally around the fuse core 23 which is composed of a suitable dielectric material such as polyester glass. The core 23 serves as a support for the relatively long, thin fuse wires and, due to its composition, improves the low current interrupting ability of the fuse. When an overload of sufficient magnitude causes the wires 24 to melt, some gas is evolved from the core 23 due to the action of high voltage which is cooled by the sand 27 and fulgurite, and silver vapor is dispersed through the sand particles. The intermediate portion of each wire 24 is of smaller diameter in order to confine the vaporization of the fuse to the sand'filled portion of the fuse.

Moreover, in accordance with this invention the fusible strain'element 18, which is disposed, preferably spirally within the bore.28 of the core 23, includes an upper end portion 35 which extends between adjoining interfaces of the annular contact 33 and the ferrule 25, thereby providing a good electrical path with the ferrule as well as with the end portions of the wires 24 which likewise contactthe ferrule. As shown in FIG. the lower end of the fusible strain element 18 includes an end portion 36 which is of slightly smaller diameter that the remaining part of the element 18 and is joined in a suitable manner such as cold welding at a joint 37.

The plug 30 comprises a longitudinal or body portion 38 which has opening means including a bore 39Jextending from the lower end of the fuse l4 and aligned with a hole 40 in the ferrule 26. The upper end of the bore '39 is closed by an end wall 41. The opening means also includesa pair of aligned apertures 42 disposed Thus, the current path extends bewteen the lower. end

portion of the fuse element 24, the lower end of the fusible strain element 18, through the ferrule 26, the conductor 43, and the loop 46. v

v In operation, the fuse 14 is disposed (FIG. 1) between the contact arms 12 and 13 so thatthe arms 12 applies a biasing force to the loop 46. The lower end portion 36 of the fusiblestrainelement 18, being disposed in the aligned apertures 42, 44, and 45, has a shear load applied to the end portions 36 at the loca tions of interface between the tubular conductor 43 and the plug 30. In this manner a greater withdrawal load may be applied by the contact arm 12 than would be possible if the end portion 36 were secured to the conductor 43 in tensiomWhen an overload current of sufficient magnitude causes the fuse element 24 to melt and disintegrate, the current path than flows through the fuse element 24 as well as the end portion 36 of preferably on diametrically opposite sides of the bore 39. A conductor 43 of tubular construction extends through the hole 40 and into thebore 39. The conductor 43 likewise includes a pair of apertures 44 and 45 which, when the conductor is disposed within the bore, are preferably aligned with the apertures 42 of the plug 30.

The end portion 36 of the fusible strain element 18 extends through the aligned apertures 42, 44, 45, and

any excess portion is wrapped around the plug (FIG. 5). The apertures 42 are then sealed with a suitable material such as a sealing'cement.

As shown in FIG. 3 the plug 30 is retained in place within the end of the bore 28 of the core 23 by the ferrule 26 which in turn is secured on the end of the fuse tube 22 by a suitable adhesive material. The conductor 1 43 comprises a loop 46 of wire one end of which is seat 49 between the ferrule 26 and the fuse tube 22, the

assembly of which is secured together by a suitable adhesive material and magnetic or mechanical crimping.

smaller diameter. The end portion 36 vaporizes and thereby eliminates the means for retaining the conductor 43 in tact, whereuponthe force applied by the contact arm 12 withdraws the conductor 43 from the end of the fuse l4.

In summary the dropout fuse structure of this invention is characterized by a new and improved release means for the body of the fuse byproviding a greater holding force for a smaller resistance element having a shear rather than a tension loading condition, whereby fuses of a lower full load rating may be provided by providing a fmer resistance wire with a shear load condition. v

What is claimed is: i

1 A dropout fuse structure comprising a fuse tube, first and second ferrules at the ends of the fuse tube, a core composed of electrically insulating material, the core having a'first'bore, a plug in at least one end of the bore, each plug having a second bo're,'a fusible strain element extending through'the first bore and having opposite end portions in operative electrical contact with the corresponding ferrules, a fuse element mounted on the exterior of the core and having opposite end portions secured to the corresponding ferrules,

into the second bore of a plug, a conductor connected to said end portion of the fusible strain element and extending'outwardly from the plug, and an axially movable member secured to the conductor operative to dislodge the conductor from the plug upon fusion of the fusible strain element.

2. The dropout fuse structure of claim 1 in which ferrule at the end of thefuse tube including the conductor comprises a hole aligned with the second bore.

4. The dropout fuse structure of claim 3 in which the holes are disposed in the plug at diametrically opposite sides of the second bore, the condcutor comprisingaperture means aligned with the holes, and the fusible strain element extendingthrough the holes and aperture means, whereby a shear loading on the fusible strain element exists between the plug and the conduc-- tor. 5. The dropout fuse structure of claim 4 in which the diameter of the portion of the fusible strain element extending through the holes and aperture means is less than the remaining portion thereof.

3 ,852,696 r 5 v 6 6. The dropout fuse structure of claim 5 in which the which the axialy movable member is secured. portion of the fusible strain element fuses when a current overload condition prevails.

7. The dropout fuse structure of claim 5 in which the loop conmcted to the correbpondmg ferrule conductor comprises an electrically conductive loop to 5 8. The dropout fuse structure of claim 7 in which the 

1. A dropout fuse structure comprising a fuse tube, first and second ferrules at the ends of the fuse tube, a core composed of electrically insulating material, the core having a first bore, a plug in at least one end of the bore, each plug having a second bore, a fusible strain element extending through the first bore and having opposite end portions in operative electrical contact with the corresponding ferrules, a fuse element mounted on the exterior of the core and having opposite end portions secured to the corresponding ferrules, an end portion of the fusible strain element extending into the second bore of a plug, a conductor connected to said end portion of the fusible strain element and extending outwardly from the plug, and an axially movable member secured to the conductor operative to dislodge the conductor from the plug upon fusion of the fusible strain element.
 2. The dropout fuse structure of claim 1 in which sand occupies the portion of the fuse tube surrounding the core.
 3. The dropout fuse structure of claim 2 in which the ferrule at the end of the fuse tube including the conductor comprises a hole aligned with the second bore.
 4. The dropout fuse structure of claim 3 in which the holes are disposed in the plug at diametrically opposite sides of the second bore, the condcutor comprising aperture means aligned with the holes, and the fusible strain element extending through the holes and aperture means, whereby a shear loading on the fusible strain element exists between the plug and the conductor.
 5. The dropout fuse structure of claim 4 in which the diameter of the portion of the fusible strain element extending through the holes and aperture means is less than the remaining portion thereof.
 6. The dropout fuse structure of claim 5 in which the portion of the fusible strain element fuses when a current overload condition prevails.
 7. The dropout fuse structure of claim 5 in which the conductor comprises an electrically conductive loop to which the axialy movable member is secured.
 8. The dropout fuse structure of claim 7 in which the loop is connected to the corresponding ferrule. 